Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
  • C08L23/08—Copolymers of ethene
  • C08L23/0807—Copolymers of ethene with unsaturated hydrocarbons only containing more than three carbon atoms
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F4/00—Polymerisation catalysts
  • C08F4/42—Metals; Metal hydrides; Metallo-organic compounds; Use thereof as catalyst precursors
  • C08F4/72—Metals; Metal hydrides; Metallo-organic compounds; Use thereof as catalyst precursors selected from metals not provided for in group C08F4/44
  • C08F4/74—Metals; Metal hydrides; Metallo-organic compounds; Use thereof as catalyst precursors selected from metals not provided for in group C08F4/44 selected from refractory metals
  • C08F4/76—Metals; Metal hydrides; Metallo-organic compounds; Use thereof as catalyst precursors selected from metals not provided for in group C08F4/44 selected from refractory metals selected from titanium, zirconium, hafnium, vanadium, niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F4/00—Polymerisation catalysts
  • C08F4/42—Metals; Metal hydrides; Metallo-organic compounds; Use thereof as catalyst precursors
  • C08F4/44—Metals; Metal hydrides; Metallo-organic compounds; Use thereof as catalyst precursors selected from light metals, zinc, cadmium, mercury, copper, silver, gold, boron, gallium, indium, thallium, rare earths or actinides
  • C08F4/52—Metals; Metal hydrides; Metallo-organic compounds; Use thereof as catalyst precursors selected from light metals, zinc, cadmium, mercury, copper, silver, gold, boron, gallium, indium, thallium, rare earths or actinides selected from boron, aluminium, gallium, indium, thallium or rare earths
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
• • E—FIXED CONSTRUCTIONS
  • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
  • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
  • E01C13/00—Pavings or foundations specially adapted for playgrounds or sports grounds; Drainage, irrigation or heating of sports grounds
  • E01C13/08—Surfaces simulating grass ; Grass-grown sports grounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
  • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
  • C08J2323/04—Homopolymers or copolymers of ethene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
  • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
  • C08J2323/04—Homopolymers or copolymers of ethene
  • C08J2323/06—Polyethene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2203/00—Applications
  • C08L2203/12—Applications used for fibers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2203/00—Applications
  • C08L2203/16—Applications used for films
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2205/00—Polymer mixtures characterised by other features
  • C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2207/00—Properties characterising the ingredient of the composition
  • C08L2207/06—Properties of polyethylene
  • C08L2207/066—LDPE (radical process)
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2308/00—Chemical blending or stepwise polymerisation process with the same catalyst
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2314/00—Polymer mixtures characterised by way of preparation
  • C08L2314/06—Metallocene or single site catalysts

Definitions

• the present invention relates to a polyethylene resin with a preferably multimodal, more preferably bimodal, molecular weight and composition distribution.
• the present invention also relates to said polyethylene resin for the preparation of films.
• Polyethylene has been used in the production of various film products, such as bags and packaging. Examples of such products include shipping sack applications, fertilizer bags, insulation bags, food packaging, lamination film etc.
• Biaxially-oriented, blown polyolefin films are generally known in the art and have been used in the production of articles such as garbage bags, shopping bags, food wraps, and any number of articles requiring polymer chain orientation in both the machine direction (MD) and the transverse direction (TD) of the film.
• cast films may be processed to achieve biaxial-orientation
• blown films are generally preferred as they usually require less subsequent processing steps to achieve good mechanical properties.
• Desirable mechanical properties include dart impact, tear strength in both the machine and transverse directions, tensile strength in both the machine and transverse directions, elastic modulus, slow puncture resistance etc.
• Optical properties that are required namely transparency are measured under gloss and haze.
• Tailoring the properties of polyolefins, such as polyethylene, to fit a desired applicability is constantly ongoing.
• the objective is to have a better balance between mechanical and optical properties.
• Metallocene catalyzed polyethylene having high and medium densities are known to have good optical properties. However, for film applications, they have mechanical properties which can still be improved, in particular dart impact, tear strength and slow puncture resistance.
• polyethylene prepared with dual site catalysts in the gas phase or with Ziegler-Natta catalysts have good mechanical properties, but poorer optical properties.
• Nucleating agents are required to improve the gloss and haze. However, nucleating agents are not particularly effective for polyethylene resins. For example, for a haze of 30%, a nucleating agent cannot improve haze to less than 25%. Achieving outstanding mechanical properties such as dart impact and/or slow puncture resistance and/or tear strength, as well as good optical properties such as haze and gloss, is an objective of the present invention.
• Another objective is to also maintain good processability of the polyethylene resin compositions i.e. a high melt strength, to provide a polyethylene resin composition particularly suitable for film applications.
• the present invention provides a metallocene-catalyzed polyethylene resin having a multimodal molecular weight distribution, comprising from 45% by weight to 75% by weight of a low density fraction, said fraction having a density below or equal to 918 g/cm 3 as measured following the method of standard test ISO 1 183 at a temperature of 23 °C,
• the density of the polyethylene resin is from 0.920 to 0.945 g/cm 3 ,
• melt index MI2 of the polyethylene resin of from 0.1 to 5 g/10min measured following the method of standard test ISO 1 133 Condition D at a temperature of 190 °C and under a load of 2.16 kg;
• composition distribution breadth index (CDBI) of the polyethylene resin is below 70%, as analyzed by quench TREF (temperature rising elution fractionation) analysis.
• the polyethylene resin comprises a fraction having a higher density than the low density fraction, wherein the ratio M w of the low density fraction/M w of the higher density fraction is less than 6 and greater than 2.5;
• the present invention also provides a film comprising the metallocene- catalyzed polyethylene resin according to the first aspect of the invention.
• the present invention also provides a process for preparing a metallocene-catalyzed polyethylene resin according to the first aspect of the invention, wherein said polyethylene resin is prepared in at least two reactors connected in series in the presence of a metallocene-containing catalyst system.
• the metallocene- containing system comprises a metallocene selected from a bridged bisindenyl metallocene or a bridged bis-tetrahydrogenated indenyl metallocene or a mixture of both.
• the present invention also provides a geo-membrane produced by flat sheet extrusion or by blown sheet extrusion comprising the metallocene-catalyzed polyethylene resin according to the first aspect of the invention.
• the present invention also provides an artificial grass tufted from slit film or monofilaments comprising the metallocene-catalyzed polyethylene resin according to the first aspect of the invention.
• Figure 1 represents a graph showing the Chemical Composition Distribution (CCD) curves obtained for resin 129 with two ATREF cooling conditions (quench, 6°C/h).
• Figure 2 represents a graph showing quench ATREF profiles for resin 129 and resin 8H, and comparatively for two monomodal mPE (density 0.923 g/cm 3 and 0.934 g/cm 3 ) and bimodal PE GX4081 from Basell.
• Figure 3 represents a graph showing the Chemical Composition Distribution (CCD) curves obtained for resin 129 and resin 8H, and comparatively for two monomodal mPE (density 0.923 g/cm 3 and 0.934 g/cm 3 ) and bimodal PE GX4081 from Basell with quench ATREF.
• CCD Chemical Composition Distribution
• Figure 4 represents a graph plotting the cumulative weight fraction as a function of SCB/1000C for resin 129 and resin 8H, and comparatively for two monomodal mPE (density 0.923 g/cm 3 and 0.934 g/cm 3 ) and bimodal PE GX4081 from Basell.
• Figure 5 represents a graph plotting the cumulative weight fraction as a function of SCB/1000C for the low density fraction of resin 129 obtained with two ATREF cooling conditions (quench, 6°C/h).
• a polyolefin means one polyolefin or more than one polyolefin.
• a metallocene-catalyzed polyethylene resin having a multimodal molecular weight and composition distribution, said metallocene-catalyzed polyethylene resin comprising from 45% by weight to 75% by weight of a low density fraction, said fraction having a density below or equal to 918 g/cm 3 , for example below or equal to 916 g/cm 3 , preferably below or equal to 915 g/cm 3 , preferably below or equal to 914 g/cm 3 as measured following the method of standard test ISO 1 183 at a temperature of 23 °C,
• the density of the polyethylene resin is from 0.920 to 0.945 g/cm 3 , preferably from 0.920 to 0.940 g/cm 3 , more preferably 0.920 to 0.936 g/cm 3 ;
• M w /M n of the polyethylene is of from 2.8 to 6.0, preferably from 3.0 to 6.0, preferably from 3.0 to 5.0, preferably from 3.0 to 4.0, more preferably 3.5 to 4.0;
• melt index MI2 of the polyethylene resin of from 0.1 to 5.0 g/10min, preferably from 0.2 to 2.0 g/10min; as measured following the method of standard test ISO 1 133 Condition D at a temperature of 190 °C and under a load of 2.16 kg; and wherein the composition distribution breadth index (CDBI) of the polyethylene resin is below 70%, as analyzed by quench TREF (temperature rising elution fractionation) analysis.
• CDBI composition distribution breadth index
• metallocene-catalyzed polyethylene resin As used herein, the terms "metallocene-catalyzed polyethylene resin", “metallocene- catalyzed polyethylene” and “polyethylene resin composition” are synonymous and used interchangeably and refers to a polyethylene produced in the presence of a metallocene catalyst.
• the metallocene-catalyzed polyethylene resin comprises from 50% by weight to 75% by weight of the low density fraction, preferably from 55% to 75% by weight of the low density fraction, based on the total weight of the polyethylene resin.
• the M w of the low density polyethylene fraction is from 80 to 180 kDa.
• the CDBI of the low density polyethylene fraction is greater than 80%, preferably greater than 85%, more preferably greater than 90%, as analyzed by TREF under slow cooling conditions (cooling rate of 6°C/hour) (also referred herein as classical ATREF).
• the low density polyethylene fraction can be obtained from the metallocene-catalyzed polyethylene resin by fractionating the resin in two fractions with preparative TREF.
• composition distribution breadth index (CDBI) of the polyethylene resin is below 70%, as analyzed by quench TREF analysis.
• composition distribution breadth index (CDBI) of the polyethylene resin is of at least 30%, as analyzed by quench TREF analysis, preferably at least 35%.
• the composition distribution broadness index (CDBI) of the polyethylene resin is below 70% and above 30 %, as analyzed by quench TREF analysis.
• the polyethylene resin comprises a fraction having a higher density than the low density fraction, wherein the ratio M w of the low density fraction/M w of the higher density fraction is less than 6.0 and greater than 2.5.
• the ratio M w of the low density fraction/M w of the higher density fraction can be less than 6.0 and greater than 2.6, for example the ratio M w of the low density fraction/M w of the higher density fraction can be less than 5.50 and greater than 2.60, for example less than 5.30 and greater than 2.70.
• the metallocene-catalyzed polyethylene resin has a polydispersity index (PI) of at least 6.5, for example of at least 6.7, for example of at least 6.9, for example of at least 7.0.
• the metallocene-catalyzed polyethylene resin has a g rhe o of less than 0.90, for example less than 0.85, for example less than 0.80, for example less than 0.75.
• the metallocene-catalyzed polyethylene resin has a g rhe o of more than 0.35.
• the present invention also covers a polyethylene resin composition having:
• a dart impact (g/ ⁇ ) as measured according to ISO 7765-1 at least equal to the value expressed by the equation below (equation expresses the observed increase of dart impact for the film according to the invention as density decrease);
• d is the density expressed in g/cm 3 measured according to ISO 1 183 at a temperature of 23 °C,
• both mechanical and optical properties are measured on a 40 ⁇ thick blown film prepared with said polyethylene resin composition using a blown film line equipment having a neck-in configuration with a extrusion screw diameter of 45mm, a length to diameter ratio of the screw of 30, a die diameter of 120 mm, a blow-up ratio (BUR) of 2.5, a die gap of 1 .4 mm, a frost line height of 320 mm, and cooling air at a temperature of 20°C.
• brackets for the dart equation express the dart impact as function of density for monomodal metallocene-catalyzed polyethylene film grades. There is an at least 40 % improvement with respect to monomodal compositions of metallocene- catalyzed polyethylene resins for the density range covered by the invention.
• a dart impact strength can be at least 3.5 g/ ⁇ ⁇ and at 0.930 g/cm 3 dart impact strength can be above 4.5 g / ⁇ measured according to ISO 7765-1.
• the expression between brackets in the equation describes the increase of tear strength in machine direction as function of density, compared to monomodal metallocene-catalyzed polyethylene resins. There is at least 35 % improvement of Elmendorf tear strength for the resins according to the invention.
• an Elmendorf tear strength in the machine direction is of at least 30 N/mm measured according to ASTM D 1922;
• the composition is suitable for preparing a film having:
• V J- and at least one, preferably both, of the following optical properties:
• composition is suitable for preparing a film having:
• composition is suitable for preparing a film having :
• the composition has a melt index MI2 of from 0.1 to 5 g/10min, measured following the method of standard test ISO 1 133 condition D at a temperature of 190 °C. More preferably, compositions for blown films have a MI2 of 0.2 to 3.8 g/10min, preferably 0.2 to 3 g/10min.
• the present invention also covers a process to prepare the polyethylene resin composition according to the invention comprising
• -a polyethylene fraction A at a weight percent of from 35 to 45 of the polyethylene resin composition, having a melt index of from 1 .0 to 200 g/10min and a density of from 0.920 to 0.965 g/cm 3 ;
• a polyethylene fraction B at a weight percent of from 45 to 75, preferably 55 to 65 of the polyethylene resin composition, having a melt index of from 0.01 to 1 g/10min and a density of from 0.910 to 0.918 g/cm 3 ,
• each fraction is prepared in a different reactor of at least two reactors connected in series in the presence of a metallocene-containing catalyst system, preferably said metallocene-containing catalyst system comprising a metallocene selected from a bridged bisindenyl metallocene, a bridged bis-tetrahydrogenated indenyl metallocene or a mixture of both,
• the polyethylene resin composition having a density of from 0.920 to 0.945g/cm 3 , for example from 0.928 to 0.940 g/cm 3 , for example from 0.930 to 0.936 g/cm 3 , measured following the method of standard test ISO 1 183 at a temperature of 23 °C, a molecular weight distribution with an M w /M n of from 2.8 to 6, preferably from 3 to 6, and preferably, a melt index MI2 of from 0.1 to 5 g/10min, preferably from 0.2 to 4 g/10min, measured following the method of standard test ISO 1 133 condition D at a temperature of 190 °C.
• the metallocene can be selected from formulas (I) and (II) below.
• the invention covers in particular films prepared from this polyethylene resin composition.
• the polyethylene resin composition is a polyethylene resin composition having a bimodal molecular weight distribution i.e. consisting essentially of polyethylene fractions A and B.
• the metallocene comprises a bridged unsubstituted bis(tetrahydroindenyl), such as ethylene-bis(tetrahydroindenyl) zirconium dichloride and ethylene- bis(tetrahydroindenyl)zirconium difluoride.
• a bridged unsubstituted bis(tetrahydroindenyl) such as ethylene-bis(tetrahydroindenyl) zirconium dichloride and ethylene- bis(tetrahydroindenyl)zirconium difluoride.
• the two reactors in series are two loop reactors, more preferably two slurry loop reactors or two liquid full loop reactors i.e. a liquid full double loop reactor.
• polyethylene fraction A is produced in the first reactor and polyethylene fraction B is produced in the second reactor.
• polyethylene fraction A is not degassed.
• said polyethylene fraction B is produced in the first reactor and said polyethylene fraction A is produced in the second reactor.
• polyethylene fraction B is degassed, such that fraction A produced in the second reactor is substantially free of comonomer, particularly for polyethylene densities of fraction A higher than 0.960 g/cm 3 .
• the same conditions and properties polyethylene resin composition apply to the process for producing that resin.
• the present invention also encompasses a film comprising or consisting essentially of a metallocene-catalyzed polyethylene resin having a multimodal molecular weight distribution, said resin comprising from 45% by weight to 75% by weight of a low density fraction, said fraction having a density below or equal to 918 g/cm 3 as measured following the method of standard test ISO 1 183 at a temperature of 23 °C,
• the density of the polyethylene resin is from 0.920 to 0.945 g/cm 3 ,
• melt index MI2 of the polyethylene resin of from 0.1 to 5 g/10min measured following the method of standard test ISO 1 133 Condition D at a temperature of 190 °C and under a load of 2.16 kg;
• composition distribution breadth index (CDBI) of the polyethylene resin is below 70%, as analyzed by quench TREF (temperature rising elution fractionation) analysis.
• the invention also covers the film comprising or consisting essentially of the polyethylene resin composition wherein the film has
• dart impact strength (g/ ⁇ ) of at least 1.4 * 2.01 + - (d-0.91815 )/ with dart
• BUR blow-up ratio
• the film has:
• the film can have:
• the film has: an Elmendorf tear strength (N/mm) in the machine direction of at least d - 0.927
• the film can be a cast or blown film.
• the invention also covers the process to prepare the films.
• the same conditions and properties apply as for the polyethylene resin composition.
• the invention also encompasses the use of the polyethylene resin composition according to the invention to prepare films, in particular cast films and blown films.
• multimodal refers to the "multimodal molecular weight distribution" of a polyethylene resin, having two or more distinct but possibly overlapping populations of polyethylene macromolecules each having different weight average molecular weights.
• a bimodal polyethylene will have two polyethylene fractions A and B.
• the bimodal polyethylene resin composition in this invention preferably has an "apparent monomodal" molecular weight distribution, which is a molecular weight distribution curve with a single peak and no shoulder.
• the polyethylene resin composition preferably obtained by blending at the polyethylene particle level wherein the different fractions of polyethylene can be obtained by operating two reactors under different polymerization conditions and transferring the first fraction to the second reactor i.e. the reactors are connected in series.
• the two reactors can be operated under the comonomer/hydrogen split mode of "inverse" (also described herein as "reverse") configuration, wherein a first low molecular weight (high melt index), high density polyethylene fraction A is produced in the first reactor and a second high molecular weight (low melt index), low density polyethylene fraction B is produced in the second reactor.
• first polyethylene fraction does not need to be degassed before being transferred to the second reactor.
• Polyethylene fraction A is preferably substantially free of comonomer, particularly for densities of fraction A of at least 0.960 g/cm 3 .
• first high molecular weight, low density polyethylene fraction B is produced in the first reactor and the second low molecular weight, high density polyethylene fraction A is produced in the second reactor, in which case the first polyethylene fraction B is preferably degassed in order to substantially remove all unpolymerized comonomer and thus for said second fraction A to be substantially free of comonomer, particularly for densities of fraction A of at least 0.960 g/cm 3 .
• the polyethylene resin composition according to the invention is prepared in the presence of a metallocene-containing catalyst system.
• the metallocene comprises a bridged bis- indenyl and/or a bridged bis-tetrahydrogenated indenyl catalyst component.
• the metallocene is selected from one of the following formula (I) or (II):
• each R is the same or different and is selected independently from hydrogen or XR'v in which X is chosen from Group 14 of the Periodic Table (preferably carbon), oxygen or nitrogen and each R' is the same or different and is chosen from hydrogen or a hydrocarbyl of from 1 to 20 carbon atoms and v+1 is the valence of X, preferably R is a hydrogen, methyl, ethyl, n-propyl, iso-propyl, n-butyl, tert-butyl group; R" is a structural bridge between the two indenyl or tetrahydrogenated indenyls to impart stereorigidity that comprises a C-1 -C4 alkylene radical, a dialkyl germanium, silicon or siloxane, or an alkyl phosphine or amine radical; Q is a hydrocarbyl radical having from 1 to 20 carbon atoms or a halogen, preferably Q is F, CI or Br; and M is a transition metal Group
• Each indenyl or tetrahydro indenyl component may be substituted with R in the same way or differently from one another at one or more positions of either of the fused rings.
• Each substituent is independently chosen.
• cyclopentadienyl ring is substituted, its substituent groups must not be so bulky so as to affect coordination of the olefin monomer to the metal M.
• Any substituents XR'v on the cyclopentadienyl ring are preferably methyl. More preferably, at least one and most preferably both cyclopentadienyl rings are unsubstituted.
• the metallocene comprises a bridged unsubstituted bis-indenyl and/or bis-tetrahydrogenated indenyl i.e. all R are hydrogens. More preferably, the metallocene comprises a bridged unsubstituted bis- tetrahydrogenated indenyl. Most preferably the metallocene is ethylene- bis(tetrahydroindenyl)zirconium dichloride or ethylene-bis(tetrahydroindenyl) zirconium difluoride .
• composition distribution breadth index (CDBI) of the low density fraction is preferably above 50%, more preferably greater than 70%, preferably greater than 75%, yet more preferably greater than 80%. This can be measured by TREF analysis.
• the active catalyst system used for polymerizing ethylene comprises the above-described catalyst component and a suitable activating agent having an ionizing action.
• Suitable activating agents are well known in the art: they include aluminium alkyls aluminoxane or boron-based compounds.
• the activating agent is selected from aluminium alkyls, more preferably from one or more of TI BAL, TEAL or TNOAL. Most preferably, the activating agent is TIBAL.
• the catalyst component can be supported on a support.
• the support is silica, a modified silica alumina or a modified silica, for example MAO-modified silica or a fluorinated silica support.
• the polymerization of the metallocene-produced high density polyethylene can be carried out in gas, solution or slurry phase.
• Slurry polymerization is preferably used to prepare the polyethylene resin composition, preferably in a slurry loop reactor or a continuously stirred reactor.
• the polymerization temperature ranges from 20 to 125 °C, preferably from 55 to 105°C, more preferably from 60 to 100°C and most preferably from 65 to 98°C and the pressure ranges from 0.1 to 10 MPa, preferably from 1 to 6 MPa, more preferably from 2 to 4.5 MPa, for a time ranging from 10 minutes to 6 hours, preferably from 1 to 3 hours, most preferably from 1 to 2.5 hours.
• a double loop reactor is preferably used for conducting the polymerization. More preferably, the two reactors in series are preferably a slurry or liquid full double loop reactor wherein each loop is operated under different conditions in order to produce the polyethylene resin composition.
• the double loop reactor can be operated in the "inverse" configuration or "direct” configuration.
• the low melt index, low density fraction has a density of at least 0.910 g/cm 3 , preferably of at least 0.912 g/cm 3 and of at most 0.918 g/ cm 3 , more preferably of at most 0.916 g/ cm 3 , yet more preferably at most 0.914 g/cm 3 . Most preferably it is of about 0.915 to 0.918 g/ cm 3 .
• Fraction B has a melt index Ml of at least 0.01 g/10min, preferably of at least 0.05 g/10min, more preferably of at least 0.1 g/10min and even more preferably of at least 0.2 g/10min and of at most 1 g/10min, more preferably of at most 0.8 g/10min, even more preferably of at most 0.6 g/10min. Most preferably, the Ml is of 0.2 to 0.5 g/10min.
• the polyethylene fraction B is present at a weight percent of from 45 to 75, preferably of from 55 to 65 of the polyethylene resin composition, preferably of from 57 to 63, most preferably of from 58 to 62.
• the higher density fraction (A) has a low molecular weight.
• the high melt index, higher density fraction has a density of at least 0.920g/cm 3 , at least 0.927g/cm 3 , preferably at least 0.930g/cm 3 , for example at least 0.940 g/cm 3 , more preferably of at least 0.942 g/cm 3 , even more preferably of at least 0.945 g/cm 3 and of at most 0.965 g/cm 3 , more preferably of at most 0.962 g/cm 3 and even more preferably of at most 0.960. Most preferably it is of about 0.927 to 0.958 g/ cm 3 .
• Fraction A has a melt index Ml of at least 0.5 g/10min, preferably of at least 0.8 g/10min, more preferably of at least 1 g/10min, even more preferably of at least 5 g/10min and most preferably of at least 10 g/10min and of at most 200 g/10min, more preferably of at most 155 g/10min, even more preferably of at most 100 g/10min. Most preferably, the Ml is of 0.8 to 100 g/10min.
• the polyethylene fraction A is present at a weight percent of from 35 to 45 of the polyethylene resin composition, preferably of from 37 to 43, most preferably of from 38 to 42.
• the melt index and density of the fraction in the second reactor were determined using the following formula:
• the weight average molecular weight (M w ) of the second fraction (B) can be determined using the following formula:
• M W B (M W - W A *M WA )/(1- W A ) based on the additive rule for blends of miscible polyethylene of similar molecular weight distribution (for example, in the present case, D (M w /M n ) can be between 2.3 and 2.7), with M w being the M w of the final resin.
• the number average molecular weight M n , of fraction B can be calculated from M wB by dividing its value by 2.6.
• the polyethylene resin composition according to the invention has a density of from 0.920 to 0.945 g/cm 3 , for example of from 0.928 to 0.940 g/cm 3 , preferably 0.930 to 0.938 g/cm 3 , more preferably 0.932 to 0.936 g/cm 3 , most preferably 0.932 to 0.934 g/cm 3 .
• the type and amount of comonomers used to prepare the copolymers useful with the invention will determine the density of the copolymer.
• Examples of comonomers that may be used to prepare the resin composition of the invention include alpha-olefins having from 3 to 12 carbon atoms, in particular propylene, butene, hexene and octene. Preferably hexene is used.
• alpha-olefins having from 3 to 12 carbon atoms, in particular propylene, butene, hexene and octene.
• hexene is used.
• One of ordinary skill in the art of preparing copolymers will know how to vary the monomer feed for any particular production unit to achieve a specified density.
• the polyethylene resin composition preferably has a melt index MI2 of from 0.1 to 5, 0.1 to 4 g/10min, preferably 0.2 to 4.0 g/10min, yet more preferably 0.3 to 3.0 g/10min following the method of standard test ISO 1 133 condition D at a temperature of 190 °C. These are ranges for polyethylene resin compositions particularly suitable for film applications.
• compositions for blown films have a MI2 of 0.1 to 4 g/10min, most preferably 0.1 to 3.0 g/10min. More preferably, compositions for cast films have a MI2 of 2.5 to 5 g/10min, most preferably 2.5 to 4.0 g/10min.
• the polyethylene resin composition of the present invention preferably has a multimodal, preferably a bimodal molecular weight distribution, with an "apparent monomodal" molecular weight distribution, which is a molecular weight distribution curve with a single peak and no shoulder.
• the polyethylene resin composition has an enlarged molecular weight distribution curve due to the bimodal composition of molecular weight.
• the polyethylene resin compositions of the present invention are bimodal in composition as measured by TREF analysis.
• TREF analysis can be performed as described in Wild et al. J. Poly. Sci., Poly. Phys. Ed. Vol. 20, (1982), 441 or US patent No. 5,008,204).
• TREF profiles were obtained in analytical mode (ATREF) using two cooling conditions: quench and 6°C/h (classical ATREF).
• TREF was also operated in preparative mode (PTREF) to obtain the low density and the higher density fractions.
• TREF analysis can be performed with TREF instrument by Polymer ChAR (Valencia, Spain).
• TREF profiles can be obtained using following conditions: Quench ATREF (analytical TREF): dissolution in 1 ,2,4-trichlorobenzene (TCB) at 160°C for 1 h, detector (DRI differential refractive index), injection of the solution in the ATREF column at about 30°C. heating rate of 2°C/min up to 130°C. concentration 0.05 % w
• the composition distribution breadth index (CDBI) of the polyethylene resin is below 70%, preferably below 68% as analyzed by quench TREF, and the CDBI of the low density polyethylene fraction is greater than 70%, preferably greater than 75% , more preferably greater than 80 %, as analyzed by TREF.
• the M w /M n of the composition is of from 2.8 to 6, for example from 3 to 6, preferably 2.8 to 5.5, more preferably 2.9 to 5.0, most preferably 2.9 to 4.6, yet most preferably from 3.0 to 4.5.
• Density is measured according to ISO 1 183 at a temperature of 23 °C.
• the melt index MI2 and high load melt index HLMI are measured by the method of standard test ISO 1 133 Condition D respectively under a load of 2.16 kg and 21 .6 kg and at a temperature of 190 °C.
• the molecular weight distribution is defined by the ratio M w /M n of the weight average molecular weight M w to the number average molecular weight M n as determined by gel permeation chromatography (GPC).
• the polyethylene resin composition according to the invention has particular rheological properties.
• the resins according to the invention exhibit an enhancement of zero-shear viscosity.
• the enhancement of zero-shear viscosity is linked to g rhe o that is a quantification of the amount of long chain branching (LCB) as probed by rheological techniques.
• LCB long chain branching
• g rh eo can be determined according to the disclosure in WO 2008/1 13680:
• M w (SEC) is the weight average molecular weight obtained from size exclusion chromatography expressed in kDa, as described above,
• Density p is measured in g/cm 3 and measured according to ISO 1 183 at a temperature of 23°C.
• Zero shear viscosity ⁇ 0 in Pa.s is obtained from a frequency sweep experiment combined with a creep experiment, in order to extend the frequency range to values down to 10 "4 s "1 or lower, and taking the usual assumption of equivalence of angular frequency (rad/s) and shear rate.
• Zero shear viscosity ⁇ 0 is estimated by fitting with Carreau-Yasuda flow curve ( ⁇ -W) at a temperature of 190°C, obtained by oscillatory shear rheology on ARES-G2 equipment (manufactured by TA Instruments) in the linear viscoelasticity domain.
• Circular frequency (W in rad/s) varies from 0.05-0.1 rad/s to 250-500 rad/s, typically 0.1 to 250 rad/s, and the shear strain is typically 10 %.
• the creep experiment is carried out at a temperature of 190°C under nitrogen atmosphere with a stress level such that after 1200 s the total strain is less than 20 %.
• the apparatus used is an AR-G2 manufactured by TA instruments.
• PI Polydispersity Index
• the polyethylene resin compositions according to the invention also have good processability and high melt strength.
• the polyethylene resins of the invention have a g rhe o below 0.9, and have higher melt strength than other bimodal resins with g rhe o close to 1 (linear PE).
• Enhanced processability of the resins of the invention can also be identified by high SR ratio (HLMI/MI2) that reflects the increased shear thinning behavior of the present resins. Both high PI and low g rhe o values contribute to an enhanced shear thinning behavior.
• This processability may also be measured for the resins of the invention, in part, by their ability to be processed at relatively comparable extrusion pressures at comparable MI2 value, despite their higher molecular weight.
• the polyethylene resin compositions exhibit sufficient melt strength to enable processing at the applicable extrusion pressures.
• the polyethylene resin composition of the present invention may contain additives, in particular additives suitable for injection stretch blow moulding, such as, by way of example, processing aids, mould-release agents, anti-slip agents, primary and secondary antioxidants, light stabilizers, anti-UV agents, acid scavengers, flame retardants, fillers, nanocomposites, lubricants, antistatic additives, nucleating/clarifying agents, antibacterial agents, plastisizers, colorants/pigments/dyes and mixtures thereof.
• additives in particular additives suitable for injection stretch blow moulding, such as, by way of example, processing aids, mould-release agents, anti-slip agents, primary and secondary antioxidants, light stabilizers, anti-UV agents, acid scavengers, flame retardants, fillers, nanocomposites, lubricants, antistatic additives, nucleating/clarifying agents, antibacterial agents, plastisizers, colorants/pigments/dyes and mixtures thereof.
• Illustrative pigments or colorants include
• Pigments such as ultramarine blue, phthalocyanine blue and iron oxide red are also suitable.
• additives include lubricants and mould-release agents such as calcium stearate, zinc stearate, SHT, antioxidants such as Irgafos 168TM, Irganox 1010TM, and Irganox 1076TM, anti-slip agents such as erucamide, light stabilizers such as tinuvin 622TM and tinuvin 326TM, and nucleating agents such as Milliken HPN20ETM.
• the polyethylene resin composition according to the invention is particularly suitable for film applications i.e. to prepare films.
• it provides a good balance in both mechanical and optical properties.
• the mechanical properties are just as good, if not better, with the added advantage that the films obtained using this metallocene-catalyzed polyethylene are particularly transparent i.e. low haze.
• the present invention therefore also encompasses a film comprising the metallocene- catalyzed polyethylene resin according to the first aspect of the invention.
• the present invention therefore also relates to a film comprising a metallocene-catalyzed polyethylene resin, said resin having a multimodal molecular weight distribution,
• said resin comprises from 45% by weight to 75% by weight of a low density fraction, said fraction having a density below or equal to 918 g/cm 3 as measured following the method of standard test ISO 1 183 at a temperature of 23 °C;
• the density of the polyethylene resin is from 0.920 to 0.945 g/cm 3 ; wherein the M w /M n of the polyethylene is of from 2.8 to 6;
• melt index MI2 of the polyethylene resin of from 0.1 to 5 g/10min as measured following the method of standard test ISO 1 133 Condition D at a temperature of 190 °C and under a load of 2.16 kg;
• composition distribution breadth index (CDBI) of the polyethylene resin is below 70%, as analyzed by quench TREF (temperature rising elution fractionation) analysis.
• the films according to the invention have preferably an excellent Dart impact strength/resistance and/or excellent tear strength both in the machine and optionally transverse directions and/or excellent resistance to slow puncture, whilst also having very good optical properties, namely haze and/or gloss.
• said film has a dart impact strength (g/ ⁇ ) as measured according to ISO 7765-1 which is at least equal to the value expressed by the equation below
• d is the density expressed in g/cm 3 as measured following the method of standard test ISO 1 183 at a temperature of 23 °C.
• the film can have a dart impact strength of a value of at least 4.5 g/ ⁇ measured according to ISO 7765-1 , for example a dart impact strength of at least 4.75 g/ ⁇ , preferably at least 5 g/ ⁇ - ⁇ , more preferably at least 5.5 g/ ⁇ - ⁇ .
• said film has an Elmendorf tear strength in the machine direction (N/mm) as measured according to ASTM D 1922 that is above or equal to the value expressed by following equation: f
• the film has an Elmendorf tear strength in the machine direction of at least f
• the film can have an Elmendorf tear strength in the machine direction of at least 38 N/mm, preferably of at least 40 N/mm, measured according to ASTM D 1922.
• the film has a slow puncture resistance of at least 65 J/mm measured according to ASTM D5748, more preferably a slow puncture resistance of at least 70 J/mm, most preferably at least 75 J/mm.
• the film has a gloss of at least 40% measured according to ASTM D- 2457 at an angle of 45°, more preferably a gloss of at least 45%, preferably at least 50%.
• the film has a haze of less than 20% measured according to ISO 14782, more preferably a haze of less than 19%, preferably less than 17%, more preferably less than 16%.
• Examples of articles and products that may desirably be prepared using the polyethylene resin compositions may include blown films and cast films.
• Blown films may include, for example, films used as geoliners, i.e., in-ground liners used to prevent contamination of surrounding soil and groundwater by materials found in, and leaching from, for example, trash collection and chemical dump sites.
• Other blown film applications include apparel bags and/or coverings, bread bags, produce bags and the like.
• the polyethylene resin compositions may be used in a wide variety of thicknesses and as one or more layers of a multi-layer film construction. In other embodiments they may be used as coatings or may, as films, be coated or subjected to fluorination or other treatments to increase their barrier potential for these and other uses.
• the films are also suitable for use in or as articles designed for packaging in particular food packaging, construction, insulation, and as laminating films etc.
• Any known film blowing line equipment can be used to prepare blown films comprising the resin composition of this invention, for example MacchiO's COEX FLEX®.
• the process parameters which can be used are well-known to the person skilled in the art depending on the desired application of the film.
• the die diameter can vary from 50 to 2000 mm.
• 50 mm would be used for smaller film applications e.g. pouches for instance for medical purposes, and on the other hand 2000 mm would be used for larger applications, such as agricultural film applications.
• the blow-up ratio (BUR) can be of 1 to 5.
• the die-gap can be of 0.8 to 2.6 mm.
• the throughput can be of 10kg/h to 2000kg/h.
• the extrusion screw can have a diameter of from 30 mm to 150 mm.
• the screw is a barrier screw.
• the resin composition can also be used to prepare cast films.
• Typical cast film equipment are provided by Dolci, SML etc. Again, the skilled person would know how to run the cast film line to obtain the best possible results.
• the film is 10 ⁇ to 500 ⁇ thick, more preferably 10 to 100 ⁇ , most preferably 10 to 75 ⁇ - ⁇ .
• the polyethylene resin composition according to the invention can be used to prepare films, which are monolayered or multilayered.
• the film is monolayered.
• the monolayered film can be prepared from the polyethylene resin composition according to the invention in combination with other resins, such as LDPE, i.e. the film comprises of the polyethylene resin composition according to the invention.
• the monolayered film is prepared essentially from the polyethylene resin composition according to the invention i.e. the film consists essentially of the polyethylene resin composition according to the invention.
• the polyethylene resin composition according to the invention can be used in one or several layers, alone or combination with other resins.
• Dart impact strength, Elmendorf tear strength and slow puncture resistance are mechanical properties which may be important for polyethylene films depending on their application.
• the polyethylene resin composition used to prepare films may also exhibit similar or even improved dart impact strength when compared with prior art polyethylenes of comparable density.
• the Dart impact strength F50 of the film prepared with the resin composition according to the invention can be at least 180g (which is the weight of the hammer required to break the film for 50% of the samples - F50), preferably at least 190g, more preferably at least 200g, even more preferably at least 21 Og, most preferably at least 216g, as measured on a film of 40 ⁇ thickness.
• Dart impact strength expressed in grams per ⁇ of film thickness, g/ ⁇
• composition according to the invention can be at least 1.4 * 2.01 + - (d-0.91815 )/
• the Dart impact strength F50 is measured according to ISO 7765-1 , method A (diameter of the hammer 38.1 mm, fall height 66cm) at 23°C with 50% humidity.
• Dart impact strength F50 are measured on 40 ⁇ thick blown film prepared using a blown film line equipment having a neck-in configuration with a extrusion screw diameter of 45mm, a length to diameter ratio of the screw of 30, a die diameter of 120 mm, a blow-up ratio (BUR) of 2.5, a die gap of 1 .4 mm, a frost line height of 320 mm, and cooling air at a temperature of 20°C.
• Elmendorf tear strength was measured in the machine direction (MD) and in the transverse direction (TD). In the machine direction, the tear strength of the film prepared with the resin composition according to the invention can be at least f
• Elmendorf tear strength in N per mm of film thickness preferably at least f
• the Elmendorf tear strength of the film prepared with the resin composition according to the invention in the transverse direction is preferably at least 170 N/mm, more preferably from 180 N/mm, even more preferably at least from 190 N/mm, and most preferably at least from 200 N/mm.
• the tear strength can be up to 220 N/mm or 210 N/mm in the transverse direction.
• the slow puncture resistance of the film prepared with the resin composition according to the invention can be at least 65 J/mm of thickness of film, preferably at least 67 J/mm, more preferably at least 70 J/mm, even more preferably at least 72 J/mm and most preferably at least 75 J/mm.
• the slow puncture resistance can be up to 1 10 J/mm, preferably up to 100 J/mm or 95 J/mm.
• the polyethylene resin composition can be used to produce films that exhibit less than about 20% haze, preferably less than 19%, more preferably less than 17%, even more preferably less than 16%, most preferably less than 15%. This can be achieved without the use of any clarity-enhancing agents i.e. nucleating agents. (In any case nucleating agents in polyethylene do not improve haze by very much. For example, a nucleating may improve a haze of 30% to not less than 25%). Films of lesser thickness exhibit even less haze, which is equivalent to higher clarity/transparency. However, even films which are thicker showed improved haze values, whilst still maintaining other mechanical properties. Haze in % is measured according to ISO 14782, herein at a thickness of 40 ⁇ .
• Gloss performance is also very good for the films produced with the polyethylene resin composition of the invention, measuring at at least 40 % for a 40 ⁇ thick film.
• the gloss is preferably at least 45 %, most preferably at least 46%.
• the gloss can be up to 65%, or up to 64%. Gloss herein is measured according to ASTM D-2457 at an angle of 45°. It can be measured with reflecto meters, for example a Byk-Gardner micro-gloss reflectometer.
• Both gloss and haze are measured on 40 ⁇ thick blown film prepared using a blown film line equipment having a neck-in configuration with a extrusion screw diameter of 45mm, a length to diameter ratio of the screw of 30, a die diameter of 120 mm, a blow-up ratio (BUR) of 2.5, a die gap of 1.4 mm, a frost line height of 320 mm, and cooling air at a temperature of 20°C.
• BUR blow-up ratio
• the present invention also encompasses geo-membranes produced by flat sheet extrusion or by blown sheet extrusion comprising the metallocene-catalyzed polyethylene resin according to the first aspect of the invention.
• the present invention encompasses a geo-membrane comprising a metallocene-catalyzed polyethylene resin having a multimodal molecular weight distribution, comprising from 45% by weight to 75% by weight of a low density fraction, said fraction having a density below or equal to 918 g/cm 3 as measured following the method of standard test ISO 1 183 at a temperature of 23 °C;
• the density of the polyethylene resin is from 0.920 to 0.945 g/cm 3 ;
• M w /M n of the polyethylene is of from 2.8 to 6;
• melt index MI2 of the polyethylene resin of from 0.1 to 5 g/10min as measured following the method of standard test ISO 1 133 Condition D at a temperature of 190 °C and under a load of 2.16 kg;
• composition distribution breadth index (CDBI) of the polyethylene resin is below 70%, as analyzed by quench TREF (temperature rising elution fractionation) analysis.
• the present invention provides geo-membrane applications produced by flat sheet extrusion or by blown sheet extrusion with a polyethylene resin according to the first aspect of the invention.
• flat sheet extrusion is preferred.
• the methods used to prepare geo-membranes can be either flat sheet extrusion or blown sheet extrusion.
• an extruder can be used. Pellets can be fed into the extruder for example by a screw system, they can then heated, placed under pressure and formed into a hot plastic mass before reaching the die. Once the components are in the hot plastic state, they can be formed either into a flat sheet by a dove tail die or into a cylindrical sheet that is subsequently cut and folded out into a flat sheet.
• the hot plastic mass is fed into a dove tail die and exits through a horizontal straight slit.
• one or more extruders may be needed to feed the hot plastic mass into the die.
• High quality metal oilers placed in front of the slit are used to control the thickness and surface quality of the sheets.
• These rollers are able to sustain pressure and temperature variations without deformation and they are connected to cooling liquids.
• the rollers are designed in order to control the sheet thickness to less than 3% variation over the whole width.
• a third roller may be used to further cool the sheet and to improve its surface finish.
• the surface finish of the sheet is directly proportional to the quality of the rollers' surface.
• the evenly cooled finished material is then fed over support rollers to be wrapped onto a core pipe and rolled up.
• the hot plastic mass is fed into a slowly rotating spiral die to produce a cylindrical sheet. Cooled air is blown into the centre of the cylinder creating a pressure sufficient to prevent its collapsing.
• the cylinder of sheeting is fed up vertically: it is then closed by being flattened over a series of rollers. After the cylinder is folded together, the sheet is cut and opened up to form a flat surface and then rolled up.
• the annular slit through which the cylinder sheet is formed is adjusted to control the sheet's thickness. Automatic thickness control is available in modern plants. Cooling is performed by the cool air blown into the centre of the cylinder and then during the rolling up process.
• the geomembrane may additionally contain usual additives well known to those skilled in the art such as for example carbon black. These additives may be present in quantities generally between 0.01 and 10 weight % based on the weight of the polyethylene.
• the geomembrane may comprise from 1 to 4 weight % of carbon black, for example 2 to 3 weight%.
• the present invention also relates to yarn made with the polyethylene resin according the invention, in particular to slit film and monofilaments suitable for tufting into artificial grass or also known as artificial turf.
• the present invention also encompasses an artificial grass tufted from slit film or monofilaments comprising the metallocene-catalyzed polyethylene resin according to the first aspect of the invention.
• the present invention encompasses a yarn and preferably an artificial grass comprising a metallocene-catalyzed polyethylene resin having a multimodal molecular weight distribution, comprising from 45% by weight to 75% by weight of a low density fraction, said fraction having a density below or equal to 918 g/cm 3 as measured following the method of standard test ISO 1 183 at a temperature of 23 °C;
• the density of the polyethylene resin is from 0.920 to 0.945 g/cm 3 ; wherein the M w /M n of the polyethylene is of from 2.8 to 6;
• melt index MI2 of the polyethylene resin of from 0.1 to 5 g/10min as measured following the method of standard test ISO 1 133 Condition D at a temperature of 190 °C and under a load of 2.16 kg;
• composition distribution breadth index (CDBI) of the polyethylene resin is below 70%, as analyzed by quench TREF (temperature rising elution fractionation) analysis.
• the polyethylene for the slit film and monofilaments for the artificial grass may additionally contain usual additives well known to those skilled in the art such as antioxidants, stabilizers, processing aids, fillers, flame retardants, coloured pigments or similar. These additives may be present in quantities generally between 0.01 and 15 weight % based on the weight of the polyethylene.
• the yarn are suitable for use in artificial turfs or grasses including synthetic sporting surfaces.
• the slit film or monofilament or similar according to all aspects of the present invention may typically be in stretched form.
• the slit film or monofilament or similar may have a draw ratio in the range 1 : 3 to 1 :8, preferably 1 :3 to 1 :6, more preferably 1 :3 to 1 :4.
• polymerizations were carried out in a double loop reactor comprising 2 reactors Rx1 and Rx2 to obtain polyethylene resin compositions G to M according to the invention.
• Polymerizations were carried at a temperature of 95°C under a pressure of about 40 bars with a residence time of about 66 min in Rx1 and at a temperature of 83°C under a pressure of about 40 bars with a residence time of about 35 min in Rx2 using an ethylene-bis(tetrahydroindenyl) zirconium dichloride metallocene catalyst system with tri- isobutylaluminium (TIBAL) as the activating agent.
• TIBAL tri- isobutylaluminium
• polymerizations were carried out in a double loop reactor comprising 2 reactors Rx1 and Rx2 to obtain polyethylene resin compositions 8G, 8H, according to the invention.
• Polymerizations were carried at a temperature of 83°C under a pressure of about 40 bars with a residence time of about 64 min in Rx1 and at a temperature of 83°C under a pressure of about 40 bars with a residence time of about 34 min in Rx2 using an ethylene-bis(tetrahydroindenyl) zirconium dichloride metallocene catalyst system with tri- isobutylaluminium (TIBAL) as the activating agent.
• TIBAL tri- isobutylaluminium
• polymerizations were carried out in a double loop reactor comprising 2 reactors Rx1 and Rx2 to obtain polyethylene resin compositions 127, 128, 129, according to the invention.
• Polymerizations were carried at a temperature of 90°C under a pressure of about 40 bars with a residence time of about 1 .7 hours in Rx1 and at a temperature of 83°C under a pressure of about 40 bars with a residence time of about 0.64 hours in Rx2 using an ethylene-bis(tetrahydroindenyl) zirconium dichloride metallocene catalyst system with tri-isobutylaluminium (TIBAL) as the activating agent.
• TIBAL tri-isobutylaluminium
• the molecular weight (M n (number average molecular weight), M w (weight average molecular weight) and M z (z-average molecular weight)) and molecular weight distributions d and d' were determined by size exclusion chromatography (SEC) and in particular by gel permeation chromatography (GPC). Briefly, a GPCV 2000 from Waters was used: 10mg polyethylene sample was dissolved at 160°C in 10 ml of trichlorobenzene for 1 hour. Injection volume: about 400 ⁇ , automatic sample preparation and injection temperature: 160°C. Column temperature: 145°C. Detector temperature: 160°C.
• M n number average
• M w weight average
• M z z average
• N, and W are the number and weight, respectively, of molecules having molecular weight Mi.
• the third representation in each case (farthest right) defines how one obtains these averages from SEC chromatograms.
• h is the height (from baseline) of the SEC curve at the i th elution fraction and M, is the molecular weight of species eluting at this increment.
• melt index MI2 and high load melt index HLMI are measured by the method of standard test ISO 1 133 Condition D respectively under a load of 2.16 kg and 21 .6 kg and at a temperature of 190 °C.
• PI Polydispersity Index
• the CDBI composition distribution breadth index
• the CDBI is a measure of the breadth of the distribution of copolymer composition, with regard to the level of comonomer incorporated into the polymer, the latter reducing crystallinity of domains made from such polymer chains by means of short side chain branching as compared to crystalline homopolymer. This is described, for example, in WO 93/03093.
• the CDBI is defined as the percent by weight or mass fraction of the copolymer molecules having a comonomer contents of ⁇ 25% of the mean total molar comonomer content, i.e. the share of comonomer molecules whose comonomer content is within 50% of the average comonomer content.
• CDBI was determined from cumulative SCB distribution as obtained by TREF (temperature rising elution fraction) analysis (quench or slow cooling conditions).
• TREF temperature rising elution fraction
• the TREF analysis were performed with TREF instrument by Polymer ChAR (Valencia, Spain). The conditions of TREF were as follows.
• Quench ATREF analytical TREF: a solution of 1 mg/ml of polyethylene resin in 1 -2-4 trichlorobenzene (TCB) was obtained by dissolution at 160°C for one hour. The solution was injected in the ATREF column at about 30°C with a flow rate of 0.5 ml/min. The column with the precipitated polyethylene was then eluted at a heating rate of 2°C/min up to 130°C. The flow rate was 0.5ml/min during the elution step.
• TBC trichlorobenzene
• Classical ATREF a solution of 0.05 % (0.5 mg/ml) of polyethylene was prepared as described for the quench TREF at 160°C and was injected on the ATREF column and allowed to slowly cool (at 6°C/h) from 100 to 30°C. The flow rate during heating from 30°C to 120°C was 0.4 ml/min and the heating rate was 1 °C/min.
• PTREF preparative TREF: The sample (about 6 g) was dissolved in xylene at 130°C at a concentration of 1 g/100 ml. The hot solution (stabilized with 1000 ppm Irganox 1010) was loaded into the inner part of the glass column of the PTREF apparatus at a temperature of 130°C. The PTREF column was then cooled at a rate of 2.4 °C/h down to 30°C (42 h).
• the low density fraction was recovered by heating to a temperature that is guided by classical ATREF in TCB : the separation temperature was about equal to the ATREF temperature corresponding to a level of SCB that will give a density about 0.92 g/cm3 (SCB 10/1000 C) minus 10°C (as PTREF is conducted in xylene not TCB). This corresponds for this PTREF apparatus to 77°C.
• the first fraction was then obtained by connecting the column to a recovery tank through which the solvent was pumped at 10 ml/min. The higher density fraction was then obtained by eluting at 100°C under similar conditions as for the first fraction. Both eluted fractions were precipitated in methanol, filtered on PTFE filters and dried.
• Figure 1 shows Chemical Composition Distribution (CCD) curves obtained for resin 129 with two ATREF cooling conditions (quench, 6°C/h).
• CCD Chemical Composition Distribution
• Figure 2 shows quench ATREF profiles for resin 129 and resin 8H, and comparatively for two monomodal mPE (density 0.923 g/cm 3 and 0.934 g/cm 3 ) and bimodal PE GX4081 from Basell.
• the ATREF profiles were bimodal for resin 129 and resin 8H.
• Bimodal PE GX4081 resin exhibits a skewed CCD curve towards high SCB with no clear sign of bimodality in quench ATREF conditions.
• g rh eo is determined according to the disclosure in WO 2008/1 13680:
• M w (SEC) is the weight average molecular weight obtained from size exclusion chromatography expressed in kDa, as described above,
• M w ( ⁇ 0 , MWD, SCB) is determined according to the following:
• M w ⁇ r 0 , MWD, SCB) exp(l .7789 + 0.199769Ln réelle + 0.209026(Lw ⁇ 0 ) + 0.955(ln p) - 0.00756 l( w i )(Ln?7 0 ) + 0.02355(ln M z f )
• M w ( ⁇ 0 , MWD, SCB) was determined by Rheological Dynamic Analysis (RDA) and is equal to M w (SEC) for linear PE (PE without LCB).
• RDA Rheological Dynamic Analysis
• SEC linear PE
• Zero shear viscosity is proportional to M w (SEC) to a power close to 3.4 th (in our case to about the 3.6 th power).
• Corrections due to molecular weight distribution and short chain branching (SCB) are used to describe zero shear viscosity as function of M w (SEC).
• Density p is measured in g/cm 3 and measured according to ISO 1 183 at a temperature of 23°C.
• Zero shear viscosity ⁇ 0 in Pa.s is obtained from a frequency sweep experiment combined with a creep experiment, in order to extend the frequency range to values down to 10 "4 s "1 or lower, and taking the usual assumption of equivalence of angular frequency (rad/s) and shear rate.
• Zero shear viscosity ⁇ 0 is estimated by fitting with Carreau-Yasuda flow curve ( ⁇ -W) at a temperature of 190°C, obtained by oscillatory shear rheology on ARES-G2 equipment (manufactured by TA Instruments) in the linear viscoelasticity domain.
• Circular frequency (W in rad/s) varies from 0.05-0.1 rad/s to 250-500 rad/s, typically 0.1 to 250 rad/s, and the shear strain is typically 10 %.
• the creep experiment is carried out at a temperature of 190°C under nitrogen atmosphere with a stress level such that after 1200 s the total strain is less than 20 %.
• the apparatus used is an AR-G2 manufactured by TA instruments.
• the polyethylene resin compositions were transformed into 40 ⁇ thick blown films using a blown film line equipment from Macchi® having a neck-in configuration with a extrusion screw diameter of 45 mm, a length to diameter ratio of the screw of 30, a die diameter of 120 mm, a blow-up ratio (BUR) of 2.5, a die gap of 1 .4 mm, a frost line height of 320 mm, and cooling air at a temperature of 20°C.
• a blown film line equipment from Macchi® having a neck-in configuration with a extrusion screw diameter of 45 mm, a length to diameter ratio of the screw of 30, a die diameter of 120 mm, a blow-up ratio (BUR) of 2.5, a die gap of 1 .4 mm, a frost line height of 320 mm, and cooling air at a temperature of 20°C.
• Lupolen GX 4081 from Basell
• Borstar FB 2310 from Borealis
• Lupolen GX 4081 processing is worst (higher extrusion pressure, less stability).
• Resins of the invention however retain very good mechanical properties, such as tear strength, slow puncture resistance and dart impact strength, whilst also having very good optical properties. This was made possible (without being bound by theory) by increasing the proportion of the low density, high molecular weight fraction in the resin composition prepared using bisindenyl or bistetrahydroindenyl metallocene based catalyst systems. It should be noted that particularly surprisingly the slow puncture for the polyethylene resin composition according to the invention was higher than for the monomodal equivalent using the same catalyst, although the opposite was actually expected.
• polyethylene resin compositions according to the invention are also easily processable due to their high melt strength. Also less neck-in was observed during blowing of the films.
• mPE1 monomodal metallocene- catalyzed polyethylene
• mPE2 monomodal metallocene-catalyzed polyethylene
• mPE2 monomodal metallocene-catalyzed polyethylene
• mPE1 failed the test with a SPNCTL below 400 hours, while mPE2 showed a SPNCTL of above 400 hours.
• the present resins should have good SPNCTL behavior, thereby showing their suitability for geomembrane application.
• Resins I and M were tested on an Oerlikon Barmag Compact line (Oerlikon Barmag, Germany), and compared with a monomodal metallocene resin A.
• the characteristic of comparative resin A are show in Table 6.
• the present resins can be run at higher speed as a + 50% speed increase was measured compared to resin A (100 m/min vs 67m/min).
• Table 1a
• CDBI Rx2fraction determined by classical ATREF cooling rate 6°C/hour

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